In the German patent DE 44 26 020 A1 a method is described, wherein the operational capability of a catalytic converter disposed in an exhaust gas region of an internal combustion engine is monitored. The monitoring is implemented on the basis of the increase in temperature, which occurs in the catalytic converter due to the exothermal conversion of oxidable exhaust gas components. Two temperature signals are ascertained, whereby the first temperature signal is based on the measurement of the temperature downstream after the catalytic converter, and the second temperature signal is calculated with the aid of a model.
A method to operate a catalytic converter, which is used to purify the exhaust gas of an internal combustion engine, and a device to implement the method have become known from the German patent DE 10 2004 031 624 A1. Provision is made in said device for an open-loop or closed-loop control of a reagent substance fill level in the catalytic converter to a specified storage set point. The targeted specification of the storage set point assures on the one hand that a sufficient quantity of the reagent substance is available to remove as completely as possible at least one undesirable exhaust gas component and on the other hand that a reagent substance slip is avoided. A model of the catalytic converter is described, which ascertains the reagent substance fill level in the catalytic converter on the basis of the reagent substance stream flowing into the catalytic converter, if need be the NOx mass flow flowing into the catalytic converter, if need be the NOx mass flow leaving the catalytic converter and if need be a reagent substance slip.
In the German patent DE 10 2005 014 662 A1, a method to diagnose an exhaust gas treatment device for the conversion of at least one undesirable exhaust gas component contained in the exhaust gas region of an internal combustion engine and a device to implement the method are described, wherein a measurement for the current conversion of the undesirable exhaust gas component is ascertained from an exhaust gas component, which is ascertained upstream before the exhaust gas treatment device and measured downstream after the exhaust gas treatment device. Provision is made, for example, for the NOx concentration or the NOx mass flow to be the exhaust gas component. Provided that the measurement for the conversion undershoots a threshold value, which can be, for example, definitely specified or specified as a function of operating parameters of the internal combustion engine and/or as parameters of the exhaust gas, an error signal is provided.
Finally the German patent DE 102 54 843 A1 describes a method to monitor an exhaust gas treatment system, to which a reducing agent is supplied. The quantity of the reducing agent, which is supplied, is changed in the diagnosis. An error is detected if due to the specified change in the reducing agent, a signal of an exhaust gas sensor disposed after the exhaust gas treatment system likewise changes in an unexpected manner.
The task underlying the invention is to specify a method to diagnose an exhaust gas sensor disposed in the exhaust gas region of an internal combustion engine as well as a device to implement the method, which has the least possible error rate.
This task is solved in each case by the characteristics specified in the independent claims.